Alkalinity & Chlorine levels stay low

Hi guys I'm new here, I gotta question no matter what do I can't get my Alkalinity levels up there r either 0 or at best .50 both r low of course. I have put in sodium bicarbonate in one night a 2kg 4.4 pounds with no increase in level reading. I have also a low chlorine problem unless I shock the pool the the levels go up but only for a day I got a stabilizer tabs from the pool store don't know the level or cya is but the tab is mostly gone.i use chlorine pucks. My pool size is 24' Above ground round pool with average pool depth of 4 feet with good circulation very clean & clear & no smell. I have a sand filter. I hope I gave u the right info u new to help me out .the PH reading r good at 7.2 to 7.8
Dave